Recently, in the field of machine tools, machine tools are equipped with CCD cameras that capture the image of a given subject (for example, workpieces, fixtures, tables, tools, etc), create two-dimensional data, and, based on the two-dimensional data created through these CCD cameras, carry out actions such as three-dimensional measurement, creating three-dimensional data, confirming correct setup of workpieces and checking for tool and workpiece collision.
Thus, in order to carry out the above processes at a high level of accuracy, a calibration process must be conducted, to find accurate camera parameters for the CCD camera in advance. Moreover, camera parameters have intrinsic parameters, which are parameters inherent to the camera, and extrinsic parameters, which show the camera's location and position in the global coordinate system.
In order to find these camera parameters, conventionally, a calibration board that has checkered calibration pattern on its top surface is usually used, and the invention proposed in this document is a different type than the conventional calibration method, which uses this checkered calibration pattern.
An example of this process is: capturing the image of the calibration pattern of the calibration board with the CCD camera, creating two-dimensional data, and based on the created two-dimensional data, extracting the lattice points of the checkered pattern, which are the feature points of the calibration pattern, and calculating the two-dimensional coordinates. The intrinsic and extrinsic parameters are calculated based on the calculated two-dimensional coordinates of the lattice points, and the three-dimensional coordinates (three-dimensional coordinates in the global coordinate system) of said lattice points that occur in the predefined space of placement of the calibration boards. Moreover, the calibration pattern's image must be captured from many different directions by changing the placement of the calibration board.
Additional information about the above calibration method is shown in other documents such as Japanese Unexamined Patent Application Publication No. 2005-250628.